Process for electroslag-remelting of metals, in particular, steel

ABSTRACT

A process and apparatus for heating steel ingots produced in an electroslag-remelting process. An electrode consisting of a steel of predetermined composition is remelted in an electroslagremelting process. A slag composition is stored in a water-cooled mold and the electrode is inserted into this slag composition and an electric current is passed through the electrode thereby melting it. The molten metal settles in the mold and solidifies therein. A base plate supports the ingot formed by the solidification of the molten metal in the mold while the distance between the top of the slag layer and the top of the molten metal remains constant by increasing the distance between the mold and the base plate, thereby causing the solidified metal to exit from the mold as a solidified metal ingot. Means are provided for heating the exposed surfaces of the metal ingots exiting from their molds.

United States Patent Schneidhofer 51 Apr. 9, 1974 FOREIGN PATENTS OR APPLICATIONS 1,103,350 2/1968 Great Britain 164/52 [75] Inventor: Adolf Schneidhofer, Kapfenberg, Primary Examiner-J. Spencer Overholser Austria Assistant Examiner-John E. Roethel [73] Assignee: Fa. Gebr. Boehler & C0. AG,

Kapfenberg, Austria [57] ABSTRACT A process and apparatus for heating steel ingots pro- [22] plied: Sepl- 11, 1972 duced in an electroslag-remelting process. An elec- [21] APP] 289,372 trode consisting of a steel of predetermined composition is remelted in an electroslag-remelting process. A Related Apphcanon Data slag composition is stored in a water-cooled mold and [63] Continuation of Ser. No. 72,783, Sept. 16, 1970, the electrode is inserted into this slag composition and abandonedan electric current is passed through the electrode n thereby melting it. The molten metal settles in the Forelgn Appllcatlon Priority Data mold and solidifies therein. A base plate supports the Sept. 18, 1969 Austria 8826/69 ingot formed by the solidification of the molten metal in the mold while the distance between the top of the [52] US. Cl. 164/52 slag layer and the top of the molten metal remains [51] Int. Cl B22d 27/02 constant by increasing the distance between the mold [58] Field of Search 164/52, 252 and the base plate, thereby causing the solidified metal to exit from the mold as a solidified metal ingot. [56] References Cited Means are provided for heating the exposed surfaces UNITED STATES PATENTS of the metal ingots exiting from their molds.

3,713,476 l/1973 Paton et al 164/52 2 Claims, 3 Drawing Figures 3Q we "tfi L 17 20 Z7 ii- 12 PATENTEBAPR 9 I974 SHiU 1 OF 2 Fig.1

Inventor:

M011 MM/0mm Attornev:

PATENIEDAPR 9 i974 SHEET 2 [IF 2 This is a continuation of application Ser. No. 72,783 filed on Sept. l6, l970, now abandoned.

BACKGROUND OF THE INVENTION The invention relates to a process for electroslagremelting of metals, in particular, steel. An electrode consisting of substantially the composition of the end product is mounted in an electroslag-remelting installation. This installation comprises a water-cooled mold and a base plate mounted underneath the mold. Installations of this type are, for example, disclosed in the US. Pat. application Ser. No. 773,622, filed Nov. 5, 1968, which is co-assigned to the assignee of the instant application. The mold in this type of installation contains liquid slag and the electrode is immersed in this liquid slag. An electric current is passed through the electrode and causes the same to melt within the mold thereby forming within the mold liquid molten metal which solidifies within the mold and thus forms a solid metal ingot which exits from the bottom of the mold and is supported on the aforementioned base plate.

In the aforedescribed known installation forming part of the prior art, the metal ingot which exits from the water-cooled mold comes into direct contact with the ambient atmosphere, and as a consequence of this, the metal ingot is intensely cooled at its lower end by the air, in particular, when this exposed end has acquired a substantial length. In the event the steel in question consists of a type of steel which is sensitive to heat cracking then the strong cooling effect causes substantial cooling cracks in the meta] ingot. Other types of steels, even when they are to be hot-worked immediately after the remelting process, must, due to the low temperature attained by the metal ingot due to the afqgementioned cooling effect, be carefully re-heated pridl" to the hot working step in order to avoid heat cracks.

SUMMARY OF THE INVENTION It is, therefore, a general object of this invention to provide a process and. installation to avoid the aforedescribed drawbacks.

In accordance with the invention, there is provided a process for electroslag-remelting of steels, wherein the metal ingot exiting from the mold is maintained in its heated condition or is additionally heated. In the process in accordance with the invention, it is advantageous to maintain the steel ingots exiting from the mold at a temperature of at least 500C. If this minimum temperature is maintained, then even with those steels favoring segregation of metals such as, for example, nickel-, molybdenum-, and vanadium-alloyed steels, can be produced with the process of the invention while avoiding the phase segegations which cause undesirable internal tensional forces.

BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated by way of example in the accompanying drawing which forms part of this application and in which:

FIG. 1 is a schematicelevational cross-sectional view of an arrangement in accordance with the invention;

FIG. 2 is a plan view of the two ring halves illustrated in FIG. 1; and

FIG. 3 is a schematic elevational sectional view of an alternate embodiment of the arrangement of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawing and, in particular, to FIGS. 1 and 2 thereof, there is illustrated an electrode 10 consisting of a steel having a composition which substantially corresponds to the composition of the ingot representing the end product of the process. This electrode 10 is concentrically mounted with respect to the cylindrical walls 21 of a water-cooled mold being generally designated with the reference numeral 20. Water or some other suitable cooling medium is adapted to flow through the hollow space defined by the walls 21 of the mold 20. The electrode 10 is adapted to have its lower end immersed into a layer of liquid slag 1 1 floating on top of a mass of molten metal 12 as shown in FIG. 1 of the drawing. The metal ingot 13 which is formed due to the solidification of the molten metal 12 within the mold 20 comes to rest on a horizontally disposed base plate 32 preferably consisting of copper. An electric current is passed through the electrode 10 from a source of electrical power (not illustrated) such as, for example, the secondary winding of a transformer, through an electrical cable 30. The other pole of the source of electric power (not illustrated) is connected via a cable 31 with the base plate 32. During the remelting process of the electrode 10, the relative height of the latter with respect to the mold 20 is continuously adjusted by cable suspension means (not illustrated) so that the electrode 10, on the one hand, is immersed with its lower end in the liquid slag 11 which floats on top of the liquid metal 12 (serving to clean and protect the molten steel) and thereby maintains the required distance between the end of the electrode 10 and the level of the molten steel 12 and, onthe other hand, with the exception of the initial phase of the remelting process, the position of this level of the molten metal 12 relative to the mold 20 remains unchanged. As soon as the distance between the lower end of the mold 20 and the base plate 32 has become larger than the distance h corresponding to the height of the two-piece ring 40, then the latter can be manually placed around the portion of the solidified ingot 30 which extends from the mold 20 in such a way that the front faces 41 of the two-piece ring 40 come in contact with each other. The two halves forming the two-piece ring 40 have an outer cover 42 consisting preferably of sheet metal, the cover defining a hollow space within the two-piece ring 40. This hollow space is filled with a heat-insulating material 43, for example, asbestos. In order to facilitate the manual handling of the two-piece ring 40, each half is provided with two hand grips 44 as shown in FIG. 2. g

FIG. 3 illustrates an alternate embodiment of the arrangement of this invention. In this embodiment, the two-piece ring has been replaced by a plurality of pipe members 50, 50, 50". which telescopically interact with each other. The mold 20' has a flange 22 at its lower end. Each pipe member 50, 50', 50". is provided at its lower end with a flange 53. On the top of the upper pipe member 50 there is mounted a preferably two-piece ring member 52 thereon by means of a plurality of bolts 51 and nuts 51. The inner diameter of the two-piece ring 52 is somewhat smaller than the inner diameter of the upper pipe member 50 and thus extends over the flange 22 of the mold Each one of the lower pipe members 50, 50, 50". are provided at their upper ends with inner projections 54 which are adapted to engage the upper surfaces of the flanges 53 as shown in FIG. 3. As the mold 20 is gradu' ally moved upwardly as the length of the ingot 13 increases, the flange 22 will abut against the lower surface of the ring 52 and thereby raise gradually the pipe member 50. A further raising of the mold 20 will eventually cause an abutting between the flange 53 of the pipe member 50 and the projection 54 of the pipe member 50', etc., thereby raising the assembly of pipe members 50, 50', 50". telescopically. At the termination of the remelting process, the innermost pipe member 50 is removed from the mold 20' by unscrewing the nuts 50 and removing the two-piece ring member 52. Thereafter the solidified ingot 13 can be removed. It can thus be noted that during the actual remelting process, the pipe members 50, 50', 50". are raised gradually by the mold 20. As is illustrated in FIG. 3, the individual'pipe members are hollow and are filled with a heat-insulating material, for example, asbestos. As can be noted from FIG. 3, the successive pipe members 50, 50', 50". each have a larger diameter than the preceding pipe member, thus creating in each instance a larger distance between the ingot l3 and the respective pipe member. It is also possible, to provide a similar arrangement wherein the pipe member having the largest internal diameter is the one that is secured to the mold and the other successive pipe members have each a smaller diameter thereby creating a gradually smaller distance between the pipe members and the cast ingot.

As can be noted from FIGS. 1 and 3, the two-piece ring member 40 as well as the two-piece ring member 50 can be provided with electrical heating cables 45, respectively 56, which are connected to a source of electrical power (not illustrated). Thus, the ingot l3 exiting from the mold 20, respectively 20', can be additionally heated by means of the afore-described auxiliary heating arrangement.

Alternately, the auxiliary heating of the ingot exiting from the mold can be accomplished by means of ringshaped gas burners (not illustrated).

The process and arrangements of the present invention improve the quality of the metal ingots produced by the remelting process, in particular, those metal ingots having a considerable length. Thus, the process of the invention ensures the avoidance of tension cracks and also ensures the avoidance of reheating cracks without requiring an auxiliary reheating oven. In the event the steel ingots produced with the process of the invention are to be hot-worked immediately after the termination of the remelting process, the improvement provided by the invention makes it possible, due to the retention of heat energy within the ingot, to require substantially less heat energy (respectively equivalent electrical energy) to raise the ingot to the forging temperature, than comparable methods which do not use the improvement of the arrangement and process of the invention.

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

What is claimed is:

1. In a process for electroslag-remelting of metals and, in particular, steel wherein an electric current is passedthrough at least one electrode consisting of the metal to be remelted, thereby melting said metal, the improvement comprising the steps of gradually moving said electrode downwardly at a rate corresponding to its melting rate;

collecting said molten metal in a cooled mold wherein said metal solidifies into a metal ingot which exits from said mold;

gradually moving said mold upwardly at a rate corresponding to the solidification rate of the metal inmaintaining said ingot in a heated condition immediately after exiting from said cooled mold by placing heat insulating means around said exiting metal ingot which telescopically increase in height at substantially the same rate at which said ingot exits from said mold.

2. In a process for electroslag-remelting of metals and, in particular, steel wherein an electric current is passed through at least one electrode consisting of the metal to be remelted, the improvement as set forth in claim 1, wherein said exiting metal ingot is maintained in a heated condition by heating it with additional heating means which are operatively mounted in said heat insulating means. 

2. In a process for electroslag-remelting of metals and, in particular, steel wherein an electric current is passed through at least one electrode consisting of the metal to be remelted, the improvement as set forth in claim 1, wherein said exiting metal ingot is maintained in a heated condition by heating it with additional heating means which are operatively mounted in said heat insulating means. 